1. Field of the Invention
The present invention relates to a voltage detection circuit for high-accurately detecting a voltage between two inputs, an overcurrent detection circuit having the voltage detection circuit, a charging current control system having the voltage detection circuit, and a voltage detection method for those circuits and system.
2. Related Art
In recent years, for the purpose of enhancing safety of equipment which is driven by a charging battery, such as a mobile phone, a demand exists for preventing flowing of an abnormal current from a charging battery to equipment and the subsequent overheating of the equipment during the use thereof. For that purpose, a fuse has hitherto been inserted between the charging battery and a component of the equipment. However, the fuse will not return to the former state once blowout. Hence an overcurrent detection circuit, which high-accurately detects the current flowing from the charging battery to the equipment, is increasingly required in place of the fuse.
In the case of detecting the current flowing from the charging battery to the equipment, a micro-resistor in such a degree as to have no influence on battery characteristic is typically inserted into a line along which the current flows from the charging battery to the equipment. Then, a voltage detection circuit detects minute voltages generated at both ends of the resistor.
Further, it is recently sought, when charging in the charging battery by use of an AC adaptor, to control the charging current flowing from the AC adaptor to the charging battery. This has required a charging current control system for high-accurately detecting the current flowing from the AC adaptor to the charging battery.
In the case of detecting the current flowing from the AC adaptor to the charging battery, a micro-resistor in such a degree as to have no influence on battery characteristics is typically inserted into a line along which-the current flows from the AC adaptor to the charging battery. Then the voltage detection circuit detects minute voltages generated at both ends of the resistor.
A voltage detection circuit to be used for an overcurrent detection circuit and a charging current control system requires to include a plurality of resistors for dividing an inputted voltage by resistance division, a voltage amplifier for amplifying the inputted minute voltage, and a comparator for comparing the amplified voltage value with a certain level to decide whether the voltage value is equal to/higher than the certain level.
The voltage value generated at each terminal of the resistor and inputted into the voltage detection circuit is excessively minute. Thereby, variations in relative errors of the plurality of resistors for dividing the inputted voltage cause variations in detected values outputted from the voltage detection circuit. Variations in input offset voltage of the voltage amplifier for amplifying the inputted minute voltage cause variations in detected values outputted from the voltage detection circuit. Variations in input offset voltage of the comparator, for comparing the amplified voltage value with a certain level to decide whether the voltage value is equal to/higher than the certain level, cause variations in detected values outputted from the voltage detection circuit.
There has been a problem due to these causes in that the conventional voltage detection circuit is not capable of outputting an accurate detection value. The same problem also occurs in an overcurrent detection circuit having the conventional voltage detection circuit, a charging current control system having the conventional voltage detection circuit, and a voltage detection method for those circuits and system.